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Abstract:

A chip handling apparatus, unit and method is presented. The chip
handling apparatus comprises a chip supply station; a chip mounting
station; and one or more chip handling units configured to pick a chip
from the supply station, transport the chip to the mounting station, and
place the chip at a mounting location; wherein each chip handling unit is
configured to temporarily retain the chip in a defined position relative
to the chip handling unit. The chip handling apparatus further comprises
means for inducing sonic vibrations in the chip when retained by one of
the chip handling units; and means for measuring the vibrations induced
in the chip.

Claims:

1. A chip handling apparatus, in particular a die bonder, comprising a) a
chip supply station, b) a chip mounting station, and c) one or more chip
handling units configured to pick a chip (5) from the supply station,
transport the chip to the mounting station, and place the chip (5) at a
mounting location, d) each chip handling unit configured to temporarily
retain the chip (5) in a defined position relative to said chip handling
unit, characterized in that e) the chip handling apparatus further
comprises i. means for inducing vibrations, in particular sonic and/or
ultrasonic vibrations, in the chip (5) when retained by one of the chip
handling units ii. means for measuring the vibrations induced in the chip
(5).

2. The chip handling apparatus according to claim 1, further comprising
discrimination means configured to determine whether the chip (5) is
damaged based upon a measurement of the vibrations induced in the chip
(5).

3. The chip handling apparatus according to one of the previous claims,
characterized in that the apparatus comprises a first chip handling unit
for picking the chip (5) from the supply station, a second chip handling
unit (94) for placing the chip (5) onto the mounting location, and
wherein the first chip handling unit is configured to hand the chip (5)
to the second chip handling unit at a first hand over location.

4. The chip handling apparatus according to claim 1 or 2, characterized
in that the apparatus comprises a first chip handling unit for picking
the chip (5) from the supply station, a second chip handling unit for
placing the chip (5) onto the mounting location, and a third chip
handling unit configured to receive the chip from the first chip handling
unit, and hand it to the second chip handling unit.

5. The chip handling apparatus according to claim 3 or 4, characterized
in that the means for inducing vibrations in the chip (5) are configured
to induce vibrations when the chip is retained by the second chip
handling unit.

6. A chip handling unit, in particular for use in a semiconductor die
bonder, said chip handling unit being configured to receive a chip (5),
in particular a semiconductor die, at a takeover location and to hand
over said chip (5) to a delivery location, said chip handling unit
comprising a) means for temporarily retaining the chip (5) in a defined
position relative to the chip handling unit, b) means for inducing
vibrations, in particular sonic and/or ultrasonic vibrations, in the chip
(5).

7. A chip handling process, in particular for a die bonding process,
comprising the steps of a) receiving a chip (5), in particular a
semiconductor die, at a takeover location by means of a chip handling
unit, b) temporarily retaining the chip (5) in a defined position
relative to the chip handling unit, c) transporting the chip (5) to a
delivery location and d) subsequently releasing the chip (5),
characterized in that e) between steps a) and d), vibrations are induced
in the chip (5), and f) the vibrations induced in the chip (5) are
measured.

8. The chip handling process according to claim 7, characterized in that
in step e), sonic and/or ultrasonic vibrations are induced in the chip
(5).

9. The chip handling process according to claim 7 or 8, characterized in
that at the delivery location, the chip (5) is placed onto a substrate or
onto another chip.

10. The chip handling process according to claim 7, 8 or 9, characterized
in that at the delivery location, the chip (5) is handed to a further
chip handling unit, in particular a place unit (94).

11. A chip handling process, in particular a die bonding process,
comprising the steps of a) picking a chip (5), in particular a
semiconductor die, from a supply station, b) transporting the chip (5) to
a mounting station by means of at least one chip handling unit, said chip
handling unit being configured to temporarily retain the chip (5) in a
defined position relative to the chip handling unit c) placing the chip
(5) onto a mounting location, characterized in that d) in step b),
vibrations are induced in the chip (5), and e) the vibrations induced in
the chip (5) are measured.

12. The chip handling process according to claim 11, characterized in
that in step d), sonic and/or ultrasonic vibrations are induced in the
chip (5).

13. The chip handling process according to one of claims 7 through 12,
further comprising the step of determining whether the chip (5) is
damaged based upon an analysis of the vibrations measured.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Swiss Patent Application No.
01265/11 filed Jul. 31, 2011, the content of which is incorporated herein
by reference.

FIELD OF THE INVENTION

[0002] The present invention pertains to the field of automation
technology. It relates to an apparatus, a unit, and a method for handling
chips, in particular semiconductor dies, in accordance with the preamble
of the independent patent claims.

BACKGROUND OF THE INVENTION

[0003] One of the biggest challenges in semiconductor packaging is
picking, handling and processing of very thin semiconductor chips. The
semiconductor chips are generally provided on a carrier tape, which
generally contains a whole semiconductor wafer that has been cut into
small chips, a process frequently referred to as dicing. The
semiconductor chips are thus commonly referred to as dies. The carrier
tape is often the same tape that supported the wafer during dicing, often
referred to as dicing tape. Die thicknesses of down to 25 μm are
common today, and there is an ongoing trend to decrease thicknesses even
further. Thicknesses of 15 μm have already been anticipated on
semiconductor manufacturer roadmaps.

[0004] Die bonders pick a single die from the carrier tape and place and
subsequently attach the picked die onto a substrate or onto another die.
In most situations, the die is attached permanently, but configurations
where dies are only attached temporarily also exist. Often, a temporary
attachment is subsequently turned into a permanent one by an additional
heating and/or pressing process. Typically, thin dies come with a wafer
backside lamination (WBL) or film over wire (FOW) lamination, i.e. an
adhesive film which is applied to an unstructured side of the wafer or
die. A process of thinning wafers, applying an adhesive film to the
wafers, mounting the wafers to a carrier tape and frame, and dicing them
into individual chips is usually referred to as wafer preparation. The
lamination, which allows for the dies to be attached due to its adhesive
properties, may be provided either between the carrier tape and the
wafer, or on a surface of the wafer facing away from the carrier tape.

[0005] Picking, placing, and transport between pick and place locations
may be carried out by a single chip handling unit in the die bonder. In
modern die bonders, however, a plurality of chip handling units is often
present: In general, picking takes place from a so called wafer table,
and is assisted by a zeroth chip handling unit, also referred to as die
ejector. The die ejector facilitates the removal of the die from the
carrier tape, e.g. by pushing the die against a first chip handling unit
called pick unit--from underneath the carrier tape. The pick unit
subsequently picks the die from the carrier tape in a pick process and
hands it over to a second chip handling unit, also referred to as place
unit. The place unit places the die onto a target position, where it is
attached. In some cases, at least one third chip handling unit--a so
called transfer unit--is provided to hand the die from the pick unit to
the place unit. An example is given in WO 07118511 A1 which is hereby
incorporated by reference in its entirety. In this manner, a die may be
attached to a substrate, e.g. a leadframe, printed circuit board,
multilayer board etc., or to another die, which itself may be have been
attached in the same way.

[0006] The fabrication of very thin wafers and the corresponding dies is
very expensive as compared to standard thickness wafers without
lamination. Sawing, picking as well as handling of very thin dies have
significant yield losses. Most of the yield is lost during wafer
preparation, die picking, or subsequent handling, resulting in damaged
dies due to typical defects as e.g. broken dies, cracked dies, chipped
dies, etc. Both place and attachment processes, in comparison, are more
reliable, giving rise to only negligible loss.

[0007] In particular for stacked die bond processes where two or more dies
are attached onto one another, attaching of a broken die may have
dramatic consequences: If a damaged die is attached onto a stack, all
previously attached dies in that stack--also referred to as package--are
lost. In an extreme situation, for example, a package consisting of 15
stacked dies may thus be lost by attaching a broken 16th die on top of
it. Assuming a pick process yield of 99%, an expected package yield drops
to 0.99 16, i.e. to 85% in this example, and to only 44% for a pick
process yield of 95%.

[0008] Known inspection methods for detecting broken, cracked or chipped
dies on die bonders are performed before the pick process--which itself
has limited yield--and are generally based on imaging a die surface under
surface illumination, followed by image processing. These inspection
techniques have limited reliability due to low crack contrast and crack
width, die warpage--also referred to as potato chip effect--and due to
the interference of crack signatures with other similar looking patterns
on the die surface.

[0009] Until recently, die bonders have not offered any mechanism or
functionality to detect die cracks prior to the bond process and after
the pick process. There were two main reasons for that: First, the
typical "direct" pick & place architecture of die bonding machines does
not allow for the usage of special (pick & place) tooling which
incorporates means for die crack detection. Second, die cracks are hard
to detect as their appearance varies extremely, both in shape, width etc.

[0010] In WO2011/018375 A1, a method and apparatus for inspecting a chip
prior to bonding by means of an optical crack detection method was
described.

SUMMARY OF THE INVENTION

[0011] It is thus an object of the invention to allow for an inspection
after picking of a die rather than--or in addition to--one before picking
of the die, e.g. on a die ejector, and thus guarantee that only undamaged
dies are attached to a substrate or a previously attached die by a die
bonder.

[0012] In addition, the invention shall allow for an identification of
damaged dies before attach, and thus to allow for omitting to place such
damaged dies onto a substrate or a stack of previously attached dies.
Ideally, inspection of the die should be possible immediately before it
is placed and subsequently attached to the substrate or to an already
attached die.

[0013] The above objects are achieved by a chip handling apparatus and a
process for handling a chip according to the independent claims.

[0014] In a chip handling apparatus and a method for handling a chip in
accordance with the present invention, acoustic and/or ultrasonic
vibrations are induced in a die, e.g. by means of an actuator, in
particular a piezo electric actuator. In a preferred embodiment of the
method and apparatus in accordance with the invention, the die is
centered on the actuator and temporarily attached by means of vacuum. As
an excitation frequency, i.e. a vibration frequency of the actuator, is
sweeped, eigenmodes of the die are excited. Eigenfrequencies
corresponding to the eigenmodes may be characterized by a mode number,
and typically range from a few 100 Hz to several 10 kHz, depending on die
size, die thickness, etc.

[0015] In an exemplary embodiment of the present invention, a chip
handling apparatus, in particular a die bonder, is presented which
comprises a chip supply station; a chip mounting station; and one or more
chip handling units configured to pick a chip from the supply station,
transport the chip to the mounting station, and place the chip at a
mounting location; wherein each chip handling unit is configured to
temporarily retain the chip in a defined position relative to the chip
handling unit, and wherein the chip handling apparatus further comprises
means for inducing sonic vibrations in the chip when retained by one of
the chip handling units; and means for measuring the vibrations induced
in the chip.

[0016] In another exemplary embodiment of the present invention, a chip
handling unit, in particular for use in a semiconductor die bonder, is
presented, which is configured to receive a chip, in particular a
semiconductor die, at a takeover location and to hand over said chip to a
delivery location, said chip handling unit comprising, means for
temporarily retaining the chip in a defined position relative to the chip
handling unit, and means for inducing vibrations, in particular sonic
and/or ultrasonic vibrations, in the chip.

[0017] In another exemplary embodiment of the present invention, a chip
handling process, in particular for a die bonding process, is presented
which comprises the steps of a) receiving a chip (5), in particular a
semiconductor die, at a takeover location by means of chip handling unit;
b) temporarily retaining the chip in a defined position relative to the
chip handling unit; c) transporting the chip to a delivery location; and
d) subsequently releasing the chip, wherein between steps a) and d),
vibrations are induced in the chip; and a vibrations induced in the chip
are measured.

[0018] The aforementioned and further objectives, advantages and features
of the invention will be detailed in the description of preferred
embodiments below in combination with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention is best understood from the following detailed
description when read in connection with the accompanying drawing. It is
emphasized that, according to common practice, the various features of
the drawing are not to scale. On the contrary, the dimensions of the
various features are arbitrarily expanded or reduced for clarity.
Included in the drawing are the following figures:

[0020]FIG. 1 shows a die bonder in accordance with an exemplary
embodiment of the present invention.

[0021]FIG. 2 shows a schematic of a preferred embodiment of a chip
handling tool for use with the present invention.

[0022]FIG. 3 shows a schematic of another preferred embodiment of a chip
handling tool for use with the present invention.

[0023]FIG. 4 shows a schematic of yet another preferred embodiment of a
chip handling tool for use with the present invention.

[0024]FIG. 5 shows a flow diagram illustrating a chip handling process in
accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 shows a schematic of an exemplary embodiment of a die bonder
in accordance with the present invention. The die bonder comprises a
plurality of chip handling units: A zeroth chip handling unit, also
called die ejector 91, ejects a die 5, which may be laminated with a WBL
or FOW lamination, from a carrier tape 59 at a wafer table. Wafer table
and die ejector 91 act as chip supply station for die bonder. After the
die 5 has been ejected, it is taken over by a first chip handling unit,
also referred to as pick unit 92. The die bonder further comprises a
second chip handling unit also referred to as place unit 94, for
transporting die 5 to and placing it onto a target position on a
substrate 6 at a chip mounting station. The pick unit 92 is capable of
rotating around a first axis, and configured to hand the die 5 over to a
third chip handling unit. Said third chip handling unit, also referred to
as transfer unit 93, is capable of rotating about a second axis, and may
thus hand the die 5 to the place unit 94. The transfer unit 93 comprises
a chip handling tool 10, which comprises at least one vacuum orifice for
temporarily attaching the die 5 to the chip handling tool 10. The
transfer unit 93 further comprises a piezo electric actuator, which is
configured to induce acoustic and/or ultrasonic vibrations in the die 5
attached to the chip handling tool 10. When the transfer unit 93 is at a
delivery location as represented by a solid line in FIG. 1, acoustic
and/or ultrasonic vibrations are induced in the die 5 by means of the
piezo electric actuator. A laser displacement meter 7 is provided to
measure the vibrations induced in die 5.

[0026] The die bonder further comprises a control system not shown in FIG.
1 to control the movements of the various chip handling units etc.

[0027]FIG. 2 shows a schematic of a preferred embodiment of a chip
handling tool 10 for use with the present invention. The chip handling
tool 10 comprises a shank 103 by means of which it may e.g. be mounted to
a chip handling unit, in particular the transfer unit 93. Piezo electric
actuator 101 is provided on the shank 103. A tube 102 consisting of a
flexible material, e.g. rubber, is mounted on the piezo electric acuator
101. The tube has a vacuum supply connection 1021, which allows for
connecting to a vacuum source in order to temporarily retain die 5 sucked
against a vacuum orifice formed at the top end of tube 102.

[0028]FIG. 3 shows a schematic of another preferred embodiment of a chip
handling tool 10' for use with the present invention. The chip handling
tool 10' again comprises shank 103 by means of which it may e.g. be
mounted to a chip handling unit, in particular the transfer unit 93.
Piezo electric actuator 101 is again provided on the shank 103. In this
embodiment, tube 102 is mounted directly on the shank 103. Again, die 5
may be sucked against the vacuum orifice formed at the top end of tube
102, and thus temporarily retained in position. Dimensions of tube 102
and piezo electric actuator 101 are chosen in such a way that a small air
gap, preferably having a length between 25 and 500 μm, preferably 50
to 200 μm results between a die sucked against the top end of tube 102
and piezo electric actuator 101.

[0029]FIG. 4 shows a schematic of yet another preferred embodiment of a
chip handling tool 10'' for use with the present invention. The chip
handling tool 10' again comprises shank 103 by means of which it may e.g.
be mounted to a chip handling unit, in particular the transfer unit 93. A
hollow piezo electric actuator 101' is provided on the shank 103, so that
a vacuum orifice is formed at an end of the hollow piezo electric
actuator 101' remote from the shank 103. A vacuum supply channel 1031 is
formed in the shank to allow for supplying vacuum to an inner side of
hollow piezo electric actuator 101'. Preferably, a layer of soft
material, e.g. rubber, is provided on the end of the hollow piezo
electric actuator 101' remote from the shank 103 in order to prevent die
5 from coming into contact with a relatively hard material of the piezo
electric actuator 101'.

[0030] As already mentioned, laser displacement meter 7 may be used to
measure vibrations induced in die 5, e.g. by measuring displacements
and/or deflections of die 5, e.g. as a function of time. The
displacements and/or deflections may be measured at a single location,
e.g. in just one corner of the die 5. Preferably, they are measured at
two or multiple locations. This way it is ensured that damages may be
detected irrespective of their location. It also allows to get an
indication of where the damage might be located. This in turn is helpful
as guidance for additional die inspection methods that may be applied.

[0031] Optical metrology based on interference may also be applied
advantageously to measure displacements and/or deflections of die 5.

[0032] Based on an input to the piezo electric actuator 101 and measured
displacement and/or deflection, one or more frequency response functions
of the die 5 are calculated. Those contain amplitude and phase
information on how the die 5 reacts to a vibration excitation. In
general, the frequency response functions show various resonance peaks
which correspond to natural eigenmodes of the die in that particular
experimental setup.

[0033] When the die 5 is damaged, e.g. when cracks, splits, chip offs or
other defects are present in the die, the frequency response functions
show deviations when compared to reference frequency response functions
of an undamaged, but otherwise identical die 5. In a damaged die 5,
mechanical stiffness and mode shapes change, so that e.g. resonance
shifts and resonance broadening due to additional damping may be
expected. Thus, damaged dies 5 may be identified by comparing measured
frequency response functions with the reference frequency function.

[0034] This is preferably accomplished by comparing response functions
over a continuous range of frequencies, preferably in a subrange between
10 Hz and 100 kHz. Alternatively, it may be accomplished by just
comparing one or more individual resonances with those from known good
dies. Preferably, a sine-wave excitation is used, and the excitation
frequency is sweeped slowly. However, a simultaneous excitation over a
range of frequencies could also be used to advantage, in particular to
allow for faster determination of the frequency response function. In
particular, one could think of a white noise excitation to excite a wide
spectrum of frequencies at once.

[0035] Instead of measuring vibrations induced in die 5 based on
measurements of displacement and/or deflection by optical means as
described above, an acoustic and/or ultrasonic receiver, e.g. a
microphone or another piezo electric element, may preferably be employed.
The vibration frequency response may thus be obtained directly without
need measurements of displacement and/or deflection. Preferably, the
vibrations induced in die 5 may also be measured by determining impedance
or an impedance spectrum of the piezo electric actuator.

[0036] Based on a discrimination between damaged and undamaged dies 5 as
described further above, exception handling controls may then allow for
avoiding attaching of broken dies 5, and for removing them from the
transfer unit 93.

[0037]FIG. 5 shows a flow diagram in accordance with certain exemplary
embodiments of the present invention. As is understood by those skilled
in the art, certain steps included in the flow diagram may be omitted;
certain additional steps may be added, and the order of the steps may be
altered from the order illustrated.

[0038] In the description so far, die 5 was retained in a defined position
relative to the transfer unit 93 by means of vacuum suction. This implies
that the die 5 is sucked against some kind of support surface in which
one or more vacuum orifices are formed, or which is defined by one or
more vacuum orifices. Preferably, the die 5 may also be retained in
position by a contactless setup, for example by a combination of
attractive, e.g. electrostatic, forces and repulsive forces, e.g. due a
flow of compressed air, to which the die may be exposed in close
proximity to a work surface of an adequately designed chip handling tool.

[0039] Although the invention is illustrated and described herein with
reference to specific embodiments, the invention is not intended to be
limited to the details shown. Rather, various modifications may be made
in the details within the scope and range of equivalents of the claims
and without departing from the invention.

[0040] In particular, although the invention was described above with
respect to semiconductor dies, it may be used for any kind of chip,
including any essentially a flat slab of material or materials that is
picked from any kind of supply carrier, in particular a tape or belt, and
placed onto a target location, in particular on a chip, substrate, tape,
belt or a storage means.